1. Technical Field
The present invention relates to a line head and an image forming device using the same, and in particular to a line head, which projects an image of a light emitting element array on a projection surface using a microlens array to form an imaging spot array, and an image forming device using the line head.
2. Related Art
JP-A-2-4546 proposes an optical writing line head having a plurality of LED array chips disposed in an LED array direction, enlargedly projecting the image of the LED array chips on a photoconductor using a positive lens disposed corresponding to the LED array chips, and thereby forming images of the light emitting dots at the ends of the adjacent LED chips so as to be adjacent to each other on the photoconductor with a distance identical to a pitch between the images of the light emitting dots of the same LED array chip, and also proposes a device using the optical writing line head as an optical reading line head with the optical path reversed.
Further, JP-A-6-344596 proposes composing the positive lens of JP-A-2-4546 as a pair of lenses so as to approximate the projection light to collimated light, thereby increasing the focal depth.
Further, JP-A-6-278314 proposes an optical writing line head having LED array chips arranged in two lines with a distance, shifting the phases of the repeated arrangements of the tow lines a half cycle from each other, and having positive lens arrays arranged in two lines corresponding to the LED array chips so that the images of the light emitting dot arrays on the photoconductor are arranged in a line.
In these past technologies, although arrays of positive lenses (systems) corresponding to the arrangement of the LED arrays are used, there is a cross talk problem that a light beam from a light emitting dot outside the axis of the LED array enters a positive lens (system) adjacent to the corresponding positive lens (system) in the lens array instead of the corresponding positive lens (system), and reaches a position different from the predetermined imaging position, which causes ghosting or loss in light intensity to problematically degrade the image quality and reduce the light efficiency.
Further, even in the case in which the images of the light emitting dot arrays are aligned on an ideal image plane at a constant pitch, if the image plane moves back and forth in the optical axis direction of the lens owing to fluctuation of the photoconductor, position error of the light emitting dot on the photoconductor is caused, which problematically causes a variation in the pitch between scan lines drawn by the light emitting dot array relatively moving in the sub-scanning direction (the pitch variation in the main-scanning direction).